The HMO/PPO Directory provides basic information on over 1,000 U.S. HMOs and Preferred Provider Organizations (PPOs). The Directory is available in print and online from Grey House Publishing.
Healthcare Integrity Data Bank: The U.S. Department of Health and Human Services maintains the
"Healthcare Integrity and Protection Data Bank" (HIPDB) as part of "a national health care fraud and abuse data collection program for reporting and disclosing certain final adverse actions taken against health care providers, suppliers, or practitioners." If you can get access to the HIPDB, you can see if an HMO has been successfully sued or disciplined for financial improprieties.
Information about these Data Banks is posted at www.npdb-hipdb.com/. However, access to the Data Bank is generally limited to government agencies, insurers and health care providers, suppliers and practitioners. If you need this sort of information, see if you can get it through one of those "eligible entities."